/*
* Copyright 2001-2004 Unicode, Inc.
* 
* Disclaimer
* 
* This source code is provided as is by Unicode, Inc. No claims are
* made as to fitness for any particular purpose. No warranties of any
* kind are expressed or implied. The recipient agrees to determine
* applicability of information provided. If this file has been
* purchased on magnetic or optical media from Unicode, Inc., the
* sole remedy for any claim will be exchange of defective media
* within 90 days of receipt.
* 
* Limitations on Rights to Redistribute This Code
* 
* Unicode, Inc. hereby grants the right to freely use the information
* supplied in this file in the creation of products supporting the
* Unicode Standard, and to make copies of this file in any form
* for internal or external distribution as long as this notice
* remains attached.
*/

/* ---------------------------------------------------------------------

Conversions between UTF32, UTF-16, and UTF-8. Source code file.
Author: Mark E. Davis, 1994.
Rev History: Rick McGowan, fixes & updates May 2001.
Sept 2001: fixed const & error conditions per
mods suggested by S. Parent & A. Lillich.
June 2002: Tim Dodd added detection and handling of incomplete
source sequences, enhanced error detection, added casts
to eliminate compiler warnings.
July 2003: slight mods to back out aggressive FFFE detection.
Jan 2004: updated switches in from-UTF8 conversions.
Oct 2004: updated to use UNI_MAX_LEGAL_UTF32 in UTF-32 conversions.

See the header file "ConvertUTF.h" for complete documentation.

------------------------------------------------------------------------ */


#include "../types.h"
#include "ConvertUTF.h"
#ifdef CVTUTF_DEBUG
#include <stdio.h>
#endif

#include <string.h>
#include <stdlib.h>

static const int halfShift  = 10; /* used for shifting by 10 bits */

static const UTF32 halfBase = 0x0010000UL;
static const UTF32 halfMask = 0x3FFUL;

#define UNI_SUR_HIGH_START  (UTF32)0xD800
#define UNI_SUR_HIGH_END    (UTF32)0xDBFF
#define UNI_SUR_LOW_START   (UTF32)0xDC00
#define UNI_SUR_LOW_END     (UTF32)0xDFFF
#define false	   0
#define true	    1

/* --------------------------------------------------------------------- */

ConversionResult ConvertUTF32toUTF16 (
                                      const UTF32** sourceStart, const UTF32* sourceEnd, 
                                      UTF16** targetStart, UTF16* targetEnd, ConversionFlags flags) {
                                        ConversionResult result = conversionOK;
                                        const UTF32* source = *sourceStart;
                                        UTF16* target = *targetStart;
                                        while (source < sourceEnd) {
                                          UTF32 ch;
                                          if (target >= targetEnd) {
                                            result = targetExhausted; break;
                                          }
                                          ch = *source++;
                                          if (ch <= UNI_MAX_BMP) { /* Target is a character <= 0xFFFF */
                                            /* UTF-16 surrogate values are illegal in UTF-32; 0xffff or 0xfffe are both reserved values */
                                            if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_LOW_END) {
                                              if (flags == strictConversion) {
                                                --source; /* return to the illegal value itself */
                                                result = sourceIllegal;
                                                break;
                                              } else {
                                                *target++ = UNI_REPLACEMENT_CHAR;
                                              }
                                            } else {
                                              *target++ = (UTF16)ch; /* normal case */
                                            }
                                          } else if (ch > UNI_MAX_LEGAL_UTF32) {
                                            if (flags == strictConversion) {
                                              result = sourceIllegal;
                                            } else {
                                              *target++ = UNI_REPLACEMENT_CHAR;
                                            }
                                          } else {
                                            /* target is a character in range 0xFFFF - 0x10FFFF. */
                                            if (target + 1 >= targetEnd) {
                                              --source; /* Back up source pointer! */
                                              result = targetExhausted; break;
                                            }
                                            ch -= halfBase;
                                            *target++ = (UTF16)((ch >> halfShift) + UNI_SUR_HIGH_START);
                                            *target++ = (UTF16)((ch & halfMask) + UNI_SUR_LOW_START);
                                          }
                                        }
                                        *sourceStart = source;
                                        *targetStart = target;
                                        return result;
}

/* --------------------------------------------------------------------- */

ConversionResult ConvertUTF16toUTF32 (
                                      const UTF16** sourceStart, const UTF16* sourceEnd, 
                                      UTF32** targetStart, UTF32* targetEnd, ConversionFlags flags) {
                                        ConversionResult result = conversionOK;
                                        const UTF16* source = *sourceStart;
                                        UTF32* target = *targetStart;
                                        UTF32 ch, ch2;
                                        while (source < sourceEnd) {
                                          const UTF16* oldSource = source; /*  In case we have to back up because of target overflow. */
                                          ch = *source++;
                                          /* If we have a surrogate pair, convert to UTF32 first. */
                                          if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_HIGH_END) {
                                            /* If the 16 bits following the high surrogate are in the source buffer... */
                                            if (source < sourceEnd) {
                                              ch2 = *source;
                                              /* If it's a low surrogate, convert to UTF32. */
                                              if (ch2 >= UNI_SUR_LOW_START && ch2 <= UNI_SUR_LOW_END) {
                                                ch = ((ch - UNI_SUR_HIGH_START) << halfShift)
                                                  + (ch2 - UNI_SUR_LOW_START) + halfBase;
                                                ++source;
                                              } else if (flags == strictConversion) { /* it's an unpaired high surrogate */
                                                --source; /* return to the illegal value itself */
                                                result = sourceIllegal;
                                                break;
                                              }
                                            } else { /* We don't have the 16 bits following the high surrogate. */
                                              --source; /* return to the high surrogate */
                                              result = sourceExhausted;
                                              break;
                                            }
                                          } else if (flags == strictConversion) {
                                            /* UTF-16 surrogate values are illegal in UTF-32 */
                                            if (ch >= UNI_SUR_LOW_START && ch <= UNI_SUR_LOW_END) {
                                              --source; /* return to the illegal value itself */
                                              result = sourceIllegal;
                                              break;
                                            }
                                          }
                                          if (target >= targetEnd) {
                                            source = oldSource; /* Back up source pointer! */
                                            result = targetExhausted; break;
                                          }
                                          *target++ = ch;
                                        }
                                        *sourceStart = source;
                                        *targetStart = target;
#ifdef CVTUTF_DEBUG
                                        if (result == sourceIllegal) {
                                          fprintf(stderr, "ConvertUTF16toUTF32 illegal seq 0x%04x,%04x\n", ch, ch2);
                                          fflush(stderr);
                                        }
#endif
                                        return result;
}

/* --------------------------------------------------------------------- */

/*
* Index into the table below with the first byte of a UTF-8 sequence to
* get the number of trailing bytes that are supposed to follow it.
* Note that *legal* UTF-8 values can't have 4 or 5-bytes. The table is
* left as-is for anyone who may want to do such conversion, which was
* allowed in earlier algorithms.
*/
static const char trailingBytesForUTF8[256] = {
  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
  1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
  2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2, 3,3,3,3,3,3,3,3,4,4,4,4,5,5,5,5
};

/*
* Magic values subtracted from a buffer value during UTF8 conversion.
* This table contains as many values as there might be trailing bytes
* in a UTF-8 sequence.
*/
static const UTF32 offsetsFromUTF8[6] = { 0x00000000UL, 0x00003080UL, 0x000E2080UL, 
0x03C82080UL, 0xFA082080UL, 0x82082080UL };

/*
* Once the bits are split out into bytes of UTF-8, this is a mask OR-ed
* into the first byte, depending on how many bytes follow.  There are
* as many entries in this table as there are UTF-8 sequence types.
* (I.e., one byte sequence, two byte... etc.). Remember that sequencs
* for *legal* UTF-8 will be 4 or fewer bytes total.
*/
static const UTF8 firstByteMark[7] = { 0x00, 0x00, 0xC0, 0xE0, 0xF0, 0xF8, 0xFC };

/* --------------------------------------------------------------------- */

/* The interface converts a whole buffer to avoid function-call overhead.
* Constants have been gathered. Loops & conditionals have been removed as
* much as possible for efficiency, in favor of drop-through switches.
* (See "Note A" at the bottom of the file for equivalent code.)
* If your compiler supports it, the "isLegalUTF8" call can be turned
* into an inline function.
*/

/* --------------------------------------------------------------------- */

ConversionResult ConvertUTF16toUTF8 (
                                     const UTF16** sourceStart, const UTF16* sourceEnd, 
                                     UTF8** targetStart, UTF8* targetEnd, ConversionFlags flags) {
                                       ConversionResult result = conversionOK;
                                       const UTF16* source = *sourceStart;
                                       UTF8* target = *targetStart;
                                       while (source < sourceEnd) {
                                         UTF32 ch;
                                         unsigned short bytesToWrite = 0;
                                         const UTF32 byteMask = 0xBF;
                                         const UTF32 byteMark = 0x80; 
                                         const UTF16* oldSource = source; /* In case we have to back up because of target overflow. */
                                         ch = *source++;
                                         /* If we have a surrogate pair, convert to UTF32 first. */
                                         if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_HIGH_END) {
                                           /* If the 16 bits following the high surrogate are in the source buffer... */
                                           if (source < sourceEnd) {
                                             UTF32 ch2 = *source;
                                             /* If it's a low surrogate, convert to UTF32. */
                                             if (ch2 >= UNI_SUR_LOW_START && ch2 <= UNI_SUR_LOW_END) {
                                               ch = ((ch - UNI_SUR_HIGH_START) << halfShift)
                                                 + (ch2 - UNI_SUR_LOW_START) + halfBase;
                                               ++source;
                                             } else if (flags == strictConversion) { /* it's an unpaired high surrogate */
                                               --source; /* return to the illegal value itself */
                                               result = sourceIllegal;
                                               break;
                                             }
                                           } else { /* We don't have the 16 bits following the high surrogate. */
                                             --source; /* return to the high surrogate */
                                             result = sourceExhausted;
                                             break;
                                           }
                                         } else if (flags == strictConversion) {
                                           /* UTF-16 surrogate values are illegal in UTF-32 */
                                           if (ch >= UNI_SUR_LOW_START && ch <= UNI_SUR_LOW_END) {
                                             --source; /* return to the illegal value itself */
                                             result = sourceIllegal;
                                             break;
                                           }
                                         }
                                         /* Figure out how many bytes the result will require */
                                         if (ch < (UTF32)0x80) {	     bytesToWrite = 1;
                                         } else if (ch < (UTF32)0x800) {     bytesToWrite = 2;
                                         } else if (ch < (UTF32)0x10000) {   bytesToWrite = 3;
                                         } else if (ch < (UTF32)0x110000) {  bytesToWrite = 4;
                                         } else {			    bytesToWrite = 3;
                                         ch = UNI_REPLACEMENT_CHAR;
                                         }

                                         target += bytesToWrite;
                                         if (target > targetEnd) {
                                           source = oldSource; /* Back up source pointer! */
                                           target -= bytesToWrite; result = targetExhausted; break;
                                         }
                                         switch (bytesToWrite) { /* note: everything falls through. */
      case 4: *--target = (UTF8)((ch | byteMark) & byteMask); ch >>= 6;
      case 3: *--target = (UTF8)((ch | byteMark) & byteMask); ch >>= 6;
      case 2: *--target = (UTF8)((ch | byteMark) & byteMask); ch >>= 6;
      case 1: *--target =  (UTF8)(ch | firstByteMark[bytesToWrite]);
                                         }
                                         target += bytesToWrite;
                                       }
                                       *sourceStart = source;
                                       *targetStart = target;
                                       return result;
}

/* --------------------------------------------------------------------- */

/*
* Utility routine to tell whether a sequence of bytes is legal UTF-8.
* This must be called with the length pre-determined by the first byte.
* If not calling this from ConvertUTF8to*, then the length can be set by:
*  length = trailingBytesForUTF8[*source]+1;
* and the sequence is illegal right away if there aren't that many bytes
* available.
* If presented with a length > 4, this returns false.  The Unicode
* definition of UTF-8 goes up to 4-byte sequences.
*/

static Boolean isLegalUTF8(const UTF8 *source, int length) {
  UTF8 a;
  const UTF8 *srcptr = source+length;
  switch (length) {
    default: return false;
      /* Everything else falls through when "true"... */
    case 4: if ((a = (*--srcptr)) < 0x80 || a > 0xBF) return false;
    case 3: if ((a = (*--srcptr)) < 0x80 || a > 0xBF) return false;
    case 2: if ((a = (*--srcptr)) > 0xBF) return false;

      switch (*source) {
        /* no fall-through in this inner switch */
    case 0xE0: if (a < 0xA0) return false; break;
    case 0xED: if (a > 0x9F) return false; break;
    case 0xF0: if (a < 0x90) return false; break;
    case 0xF4: if (a > 0x8F) return false; break;
    default:   if (a < 0x80) return false;
      }

    case 1: if (*source >= 0x80 && *source < 0xC2) return false;
  }
  if (*source > 0xF4) return false;
  return true;
}

/* --------------------------------------------------------------------- */

/*
* Exported function to return whether a UTF-8 sequence is legal or not.
* This is not used here; it's just exported.
*/
Boolean isLegalUTF8Sequence(const UTF8 *source, const UTF8 *sourceEnd) {
  int length = trailingBytesForUTF8[*source]+1;
  if (source+length > sourceEnd) {
    return false;
  }
  return isLegalUTF8(source, length);
}

/* --------------------------------------------------------------------- */

ConversionResult ConvertUTF8toUTF16 (
                                     const UTF8** sourceStart, const UTF8* sourceEnd, 
                                     UTF16** targetStart, UTF16* targetEnd, ConversionFlags flags) {
                                       ConversionResult result = conversionOK;
                                       const UTF8* source = *sourceStart;
                                       UTF16* target = *targetStart;
                                       while (source < sourceEnd) {
                                         UTF32 ch = 0;
                                         unsigned short extraBytesToRead = trailingBytesForUTF8[*source];
                                         if (source + extraBytesToRead >= sourceEnd) {
                                           result = sourceExhausted; break;
                                         }
                                         /* Do this check whether lenient or strict */
                                         if (! isLegalUTF8(source, extraBytesToRead+1)) {
                                           result = sourceIllegal;
                                           break;
                                         }
                                         /*
                                         * The cases all fall through. See "Note A" below.
                                         */
                                         switch (extraBytesToRead) {
      case 5: ch += *source++; ch <<= 6; /* remember, illegal UTF-8 */
      case 4: ch += *source++; ch <<= 6; /* remember, illegal UTF-8 */
      case 3: ch += *source++; ch <<= 6;
      case 2: ch += *source++; ch <<= 6;
      case 1: ch += *source++; ch <<= 6;
      case 0: ch += *source++;
                                         }
                                         ch -= offsetsFromUTF8[extraBytesToRead];

                                         if (target >= targetEnd) {
                                           source -= (extraBytesToRead+1); /* Back up source pointer! */
                                           result = targetExhausted; break;
                                         }
                                         if (ch <= UNI_MAX_BMP) { /* Target is a character <= 0xFFFF */
                                           /* UTF-16 surrogate values are illegal in UTF-32 */
                                           if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_LOW_END) {
                                             if (flags == strictConversion) {
                                               source -= (extraBytesToRead+1); /* return to the illegal value itself */
                                               result = sourceIllegal;
                                               break;
                                             } else {
                                               *target++ = UNI_REPLACEMENT_CHAR;
                                             }
                                           } else {
                                             *target++ = (UTF16)ch; /* normal case */
                                           }
                                         } else if (ch > UNI_MAX_UTF16) {
                                           if (flags == strictConversion) {
                                             result = sourceIllegal;
                                             source -= (extraBytesToRead+1); /* return to the start */
                                             break; /* Bail out; shouldn't continue */
                                           } else {
                                             *target++ = UNI_REPLACEMENT_CHAR;
                                           }
                                         } else {
                                           /* target is a character in range 0xFFFF - 0x10FFFF. */
                                           if (target + 1 >= targetEnd) {
                                             source -= (extraBytesToRead+1); /* Back up source pointer! */
                                             result = targetExhausted; break;
                                           }
                                           ch -= halfBase;
                                           *target++ = (UTF16)((ch >> halfShift) + UNI_SUR_HIGH_START);
                                           *target++ = (UTF16)((ch & halfMask) + UNI_SUR_LOW_START);
                                         }
                                       }
                                       *sourceStart = source;
                                       *targetStart = target;
                                       return result;
}

/* --------------------------------------------------------------------- */

ConversionResult ConvertUTF32toUTF8 (
                                     const UTF32** sourceStart, const UTF32* sourceEnd, 
                                     UTF8** targetStart, UTF8* targetEnd, ConversionFlags flags) {
                                       ConversionResult result = conversionOK;
                                       const UTF32* source = *sourceStart;
                                       UTF8* target = *targetStart;
                                       while (source < sourceEnd) {
                                         UTF32 ch;
                                         unsigned short bytesToWrite = 0;
                                         const UTF32 byteMask = 0xBF;
                                         const UTF32 byteMark = 0x80; 
                                         ch = *source++;
                                         if (flags == strictConversion ) {
                                           /* UTF-16 surrogate values are illegal in UTF-32 */
                                           if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_LOW_END) {
                                             --source; /* return to the illegal value itself */
                                             result = sourceIllegal;
                                             break;
                                           }
                                         }
                                         /*
                                         * Figure out how many bytes the result will require. Turn any
                                         * illegally large UTF32 things (> Plane 17) into replacement chars.
                                         */
                                         if (ch < (UTF32)0x80) {	     bytesToWrite = 1;
                                         } else if (ch < (UTF32)0x800) {     bytesToWrite = 2;
                                         } else if (ch < (UTF32)0x10000) {   bytesToWrite = 3;
                                         } else if (ch <= UNI_MAX_LEGAL_UTF32) {  bytesToWrite = 4;
                                         } else {			    bytesToWrite = 3;
                                         ch = UNI_REPLACEMENT_CHAR;
                                         result = sourceIllegal;
                                         }

                                         target += bytesToWrite;
                                         if (target > targetEnd) {
                                           --source; /* Back up source pointer! */
                                           target -= bytesToWrite; result = targetExhausted; break;
                                         }
                                         switch (bytesToWrite) { /* note: everything falls through. */
      case 4: *--target = (UTF8)((ch | byteMark) & byteMask); ch >>= 6;
      case 3: *--target = (UTF8)((ch | byteMark) & byteMask); ch >>= 6;
      case 2: *--target = (UTF8)((ch | byteMark) & byteMask); ch >>= 6;
      case 1: *--target = (UTF8) (ch | firstByteMark[bytesToWrite]);
                                         }
                                         target += bytesToWrite;
                                       }
                                       *sourceStart = source;
                                       *targetStart = target;
                                       return result;
}

/* --------------------------------------------------------------------- */

ConversionResult ConvertUTF8toUTF32 (
                                     const UTF8** sourceStart, const UTF8* sourceEnd, 
                                     UTF32** targetStart, UTF32* targetEnd, ConversionFlags flags) {
                                       ConversionResult result = conversionOK;
                                       const UTF8* source = *sourceStart;
                                       UTF32* target = *targetStart;
                                       while (source < sourceEnd) {
                                         UTF32 ch = 0;
                                         unsigned short extraBytesToRead = trailingBytesForUTF8[*source];
                                         if (source + extraBytesToRead >= sourceEnd) {
                                           result = sourceExhausted; break;
                                         }
                                         /* Do this check whether lenient or strict */
                                         if (! isLegalUTF8(source, extraBytesToRead+1)) {
                                           result = sourceIllegal;
                                           break;
                                         }
                                         /*
                                         * The cases all fall through. See "Note A" below.
                                         */
                                         switch (extraBytesToRead) {
      case 5: ch += *source++; ch <<= 6;
      case 4: ch += *source++; ch <<= 6;
      case 3: ch += *source++; ch <<= 6;
      case 2: ch += *source++; ch <<= 6;
      case 1: ch += *source++; ch <<= 6;
      case 0: ch += *source++;
                                         }
                                         ch -= offsetsFromUTF8[extraBytesToRead];

                                         if (target >= targetEnd) {
                                           source -= (extraBytesToRead+1); /* Back up the source pointer! */
                                           result = targetExhausted; break;
                                         }
                                         if (ch <= UNI_MAX_LEGAL_UTF32) {
                                           /*
                                           * UTF-16 surrogate values are illegal in UTF-32, and anything
                                           * over Plane 17 (> 0x10FFFF) is illegal.
                                           */
                                           if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_LOW_END) {
                                             if (flags == strictConversion) {
                                               source -= (extraBytesToRead+1); /* return to the illegal value itself */
                                               result = sourceIllegal;
                                               break;
                                             } else {
                                               *target++ = UNI_REPLACEMENT_CHAR;
                                             }
                                           } else {
                                             *target++ = ch;
                                           }
                                         } else { /* i.e., ch > UNI_MAX_LEGAL_UTF32 */
                                           result = sourceIllegal;
                                           *target++ = UNI_REPLACEMENT_CHAR;
                                         }
                                       }
                                       *sourceStart = source;
                                       *targetStart = target;
                                       return result;
}

UTF32 *MakeUTF32FromUTF8(UTF8 *string)
{
  UTF32 *ret, *tstart;
  const UTF8 *tstring = string;

  size_t string_length = strlen((char *)string);

  tstart = ret = (UTF32 *)malloc(string_length * sizeof(UTF32) + 1);

  ConvertUTF8toUTF32(&tstring, &string[string_length], &tstart, &tstart[string_length], lenientConversion);

  *tstart = 0;

  return(ret);
}


/* ---------------------------------------------------------------------

Note A.
The fall-through switches in UTF-8 reading code save a
temp variable, some decrements & conditionals.  The switches
are equivalent to the following loop:
{
int tmpBytesToRead = extraBytesToRead+1;
do {
ch += *source++;
--tmpBytesToRead;
if (tmpBytesToRead) ch <<= 6;
} while (tmpBytesToRead > 0);
}
In UTF-8 writing code, the switches on "bytesToWrite" are
similarly unrolled loops.

--------------------------------------------------------------------- */
